#define _CRT_SECURE_NO_WARNINGS 1
//a:bushiwo 
//b:shi c
//c:shi d 
//d:c hushuo
//
#include<stdio.h>
int main()
{
	int killer = 0;
	for (killer = 'a'; killer <= 'd'; killer++)
	{
		if ((killer != 'a') + (killer == 'c') + (killer == 'd') + (killer != 'd') == 3)
		{
			printf("%c", killer);
		}
	}


	return 0;
}